1. Technical Field
The present invention relates generally to a structure of a window covering, and more particularly to a TDBU (top down, bottom up) window covering which has a carriage structure.
2. Description of Related Art
A conventional TDBU (top down, bottom up) window covering includes a headrail, a middle rail, and a bottom rail, wherein a slat assembly is provided between the middle rail and the bottom rail. The conventional TDBU window covering uses two cords to move the middle rail toward the headrail or the bottom rail (i.e., the middle rail is movable in two directions), and uses other two cords to move the bottom rail toward or away from the middle rail, whereby the area shaded by the TDBU window covering could be changed at will.
However, two sets of reeling unit of a conventional TDBU window covering used for winding up the cords are installed in the headrail, which has very limited inner space to accommodate all of these components, and therefore the two sets of reeling units may interfere with each other. In other words, such arrangement is inconvenient and burdensome for assembling and even maintenance.